Open back cap



FIG. 1 is a front perspective view of my open back cap;

FIG. 2 is a right side elevational view thereof with the left side elevational view being a mirror image;

FIG. 3 is a top view thereof;

FIG. 4 is a bottom view thereof;

FIG. 5 is a front view thereof; and,

FIG. 6 is a rear view thereof. 

I claim the ornamental design for an open back cap, as shown and described. 